United States Department of Transportation
i
Analysis Procedures for Evaluating Superheavy Load Movement on Flexible Pavements, Volume V: Appendix D, Estimation of Subgrade Shear Strength Parameters Using Falling Weight Deflectometer
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2019-01-01
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[PDF-1.77 MB]
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Abstract:The movement of superheavy loads (SHLs) has become more common over the years since it is a vital necessity for many important industries, such as chemical, oil, electrical, and defense. SHL hauling units are much larger in size and weight compared to standard trucks. SHL gross vehicle weights may be in excess of a few million pounds, so they often require specialized trailers and components with nonstandard spacing between tires and axles. Accommodating SHL movements requires the determination of whether a pavement is structurally adequate and involves the analysis of the likelihood of instantaneous or rapid load-induced shear failure. As part of the Federal Highway Administration project, Analysis Procedures for Evaluating Superheavy Load Movement on Flexible Pavements, a novel methodology to estimate in-situ shear strength parameters (angle of internal friction (ϕ) and cohesion (c)) of a pavement’s subgrade (SG) layer was developed and verified. The approach is based on nondestructive falling weight deflectometer (FWD) testing undertaken at multiple load levels. The validity of the proposed approach was explored using numerical simulations of FWD tests, as well as FWD data collected from large-scale experiments on full-scale pavement structures and Accelerated Pavement Testing facilities. It was found that the proposed FWD-based methodology was able to reasonably estimate ϕ and c of an SG layer with softening behavior. Such results were achieved when the highest induced deviator stress level in the SG layer under the FWD loading was in excess of approximately 30 percent of the deviator stress at failure obtained with the proposed procedure.
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